docs: def _unescape(v):
      """Unescape characters in a TOML string."""
      i = 0
      backslash = False
      while i < len(v):
          if backslash:
              backslash = False
              if v[i] in _escapes:
                  v = v[:i - 1] + _escape_to_escapedchars[v[i]] + v[i + 1:]
              elif v[i] == '\\':
                  v = v[:i - 1] + v[i:]
              elif v[i] == 'u' or v[i] == 'U':
                  i += 1
              else:
                  raise TomlDecodeError("Reserved escape sequence used")
              continue
          elif v[i] == '\\':
              backslash = True
          i += 1
      return v